The present invention relates generally to gas turbine engines and more particularly, to centering springs used in gas turbine engines.
The rotating shafts and other rotating turbomachinery of gas turbine engines are supported from a non-rotating structure by arrays of anti-friction bearings. In many engines, anti-friction bearings are enclosed in bearing compartments that allow them to be more easily lubricated and cooled.
Many bearing compartments, especially those containing multiple damped bearings, have small interiors, making incorporation of oil jets, scoops, retaining features, seal assemblies, and other components as well as assembly, maintenance, and repair tasks difficult. In a damped bearing, the outer race is shaped to form an annular cavity between the outer race and the bearing support, which forms a squeeze film damper (SFD) when filled with a damping fluid. With this configuration, radial displacement of the outer race relative to the bearing support is restrained by squeeze film pressure. Other bearings within the compartment can be supported by a centering spring. These sprung bearings have an outer race that is typically press fit or incorporated into a monolithic centering spring, which in turn is fastened to a bearing support or clamped between a retaining nut and the bearing support. Some bearings combine the damped and sprung configuration by fitting an outer race of a bearing into a monolithic centering spring and forming a SFD between a portion of the centering spring and a static component (e.g., a casing or housing). In the sprung and damped configuration, the centering spring and SFD form a spring-damper system in which excitations are damped by the SFD.
One or more of the aforementioned bearing arrangements holds the rotor centerline of the gas turbine engine in an appropriate position and attenuates force transmission from the rotating shafts and other rotating machinery to the bearing support of the gas turbine engine. In a conventional configuration that includes two adjacent damped bearings, the centering spring spans between bearing supports, which contain fluid passages for delivering damping fluid to the outer races of each bearing. However, such conventional centering spring configurations are costly to fabricate because multiple parts with a number of tightly-toleranced interfaces must be sized, machined, and assembled. To accommodate the bearing supports without enlarging the bearing compartment, conventional centering springs are constrained in axial length. For a given spring stiffness, shorter spring lengths result in thinner and more highly-stressed beams or members. Generally, relatively thin, highly stressed members reduce the fatigue life of the centering spring whereas tight tolerances at interfaces increase cost and complexity.
Since gas turbine engine manufacturers continually seek to reduce the cost and complexity of gas turbine components while striving to increase fatigue life, a need exists for new centering spring designs that resolve the fatigue life and complexity concerns of conventional centering springs without interfering with the geometric constrains of small bearing compartments.